Comparison of silica-based poly(amine) containing ion exchangers and their guanidine derivatives for selective PGM recovery from authentic refinery process solutions

[摘要] ENGLISH ABSTRACT: The platinum group metals (PGMs: Pt, Pd, Rh, Ir, Os and Ru) occur in nature in closeassociation with other transition metals, such as Fe, Cu, Ni and Co in often largequantities. The separation and refinement of the PGMs largely uses solventextraction, and ion exchange methods and finally incorporates precipitation andredissolution steps in order to obtain the pure PGM products at the end. During therefinement, precipitation and redissolution steps, PGM losses occur which give rise toprocess effluents which are termed authentic refinery process (ARP) solutions in thisthesis. These process solutions have PGMs in low concentrations that could not berecovered by the present recovery processes. We have synthesised silica-basedpoly(amine)-containing ion exchangers (monoamine (N1); ethylenediamine (N2) anddiethylenetriamine (N3)) and their corresponding dimethylguanidine derivatives(N1G-N3G) and have tested their Pt, Pd, Rh and Ir recovery behaviour from four ARPsolutions. The ARP solutions vary considerably in compositions with the pH of thesolutions ranging between -0.6 to 5.0.Palladium showed up to quantitative extraction from ARP solutions with thehighest pH's (pH 3.2 and 5.0) with both types of ion exchangers. However, the Pt,Pd, Rh and Ir extractions were not so good under very acidic conditions (pH -0.6 and0.2) for both types of ion exchangers. Maximum extractions were achieved at 60%(Ir), 54% (Pt), 46% (Rh) and 17% (Pd) with the N3 ion exchanger. A possibleexplanation for the incomplete PGM extractions was the high unbound chlorideconcentrations competing with the ion exchanger for the binding sites as well as theunknown speciation of individual PGM complexes in the ARP solutions. An increasein extraction followed a general trend from: N1 < N2 < N3. A very good PGMselectivity over Cu, Ni, Co and Fe under very acidic conditions was demonstrated byboth types of ion exchangers. At increased pH, the selectivity dropped with the use ofpoly(amine) ion exchangers while the corresponding dimethylguanidine counterpartsretained the selectivity due to their high pKa value. Quantitative desorptions wereattained for Pd with the use of 5M HCI and the combination of 0.5M thiourea I 1 MHCI solutions for both types of ion exchangers, while 60%-90% Ir and Rh desorptionscould be achieved with 2M HN03. In terms of the re-usability of the ion exchangers,the poly(amine) ion exchange material was more stable than the dimethylguanidineion exchange material, under harsh desorption conditions (5M HCI). Overall, bestsuccessive recoveries were obtained for Pd (ca 35.0 mg/g ion exchanger) with theN3 ion exchanger after 5 cycles of adsorption and desorption.

[发布机构] Stellenbosch University